Most of piezoelectric materials, which are used for various piezoelectric devices, are lead zirconate titanate. Attempts have been made to substitute those piezoelectric materials that contain lead with a piezoelectric material that does not contain lead (lead-free piezoelectric material). This is because, it has been pointed out a risk of doing harm to an ecosystem, because a lead component within the piezoelectric material starts to dissolve into soil, if a piezoelectric device that contains lead is once disposed and exposed to acid rain. For this reason, there is proposed a lead-free piezoelectric material.
As the lead-free piezoelectric materials, there are well known, for example, materials containing as main component niobium, barium, and bismuth, and having a tungsten bronze structure.
“Japanese Journal of Applied Physics, 1987, Vol. 26, No. 5, p. 778 to 779” discloses a bismuth barium niobium oxide-based piezoelectric material. Further, Japanese Patent Application Laid-Open No. 2001-72466 discloses a material system containing as a main component barium lithium niobium oxide and as a sub-component bismuth niobium oxide.
However, in the material system disclosed in “Japanese Journal of Applied Physics, 1987, Vol. 26, No. 5, p. 778 to 779”, there was a problem in that, if bismuth component increases, although piezoelectric properties become higher, a Curie temperature is lowered, thereby being not suitable for use in high temperature.
Further, even in a material system disclosed in Japanese Patent Application Laid-Open No. 2001-72466, there was a problem in that if bismuth component increases, the Curie temperature is lowered.